Extended AV1135 with Task-specified defaults

Closed dennisdoomen#174

_pages/1100_MemberDesignGuidelines.md

@@ -46,7 +46,7 @@ You generally don't want callers to be able to change an internal collection, so
 
 ### <a name="av1135"></a> Properties, arguments and return values representing strings or collections should never be `null` (AV1135) ![](/assets/images/1.png)
 
-Returning `null` can be unexpected by the caller. Always return an empty collection or an empty string instead of a `null` reference. This also prevents cluttering your code base with additional checks for `null`, or even worse, `string.IsNullOrEmpty()`.
+Returning `null` can be unexpected by the caller. Always return an empty collection or an empty string instead of a `null` reference. When your member return `Task` or `Task<T>`, return `Task.CompletedTask` or `Task.FromResult()`. This also prevents cluttering your code base with additional checks for `null`, or even worse, `string.IsNullOrEmpty()`.
 
 ### <a name="av1137"></a> Define parameters as specific as possible (AV1137) ![](/assets/images/2.png)